युनिकोड

युनिकोड कम्प्युटरको एक अन्तर्राष्ट्रिय गुणस्तर हो जसको उदेश्य मानिसले कम्प्युटरमा भण्डारण गर्न चाहने हरेक दस्तावेजका लिपिलाई सङ्केतन (encode) गर्ने माध्यम प्रदान गर्नु हो। This includes all scripts still मा active use today, many scripts known only by scholars, र symbols which do not strictly represent scripts, like mathematics, linguistics र APL.

The creation of युनिकोड is an ambitious project to replace existing character sets, many of which are short मा size र problematic मा बहुभाषीय environments. Despite technical problems र limitations र criticism on process, today युनिकोड is considered the most complete character set र one of the largest, र has become the dominant encoding scheme मा अन्तराष्ट्रियकरण of software र multilingual environments. Many recent standards such as XML, as well as system software such as operating systems, have adopted युनिकोड as an underlying scheme to represent text.

Origin र development

It is the explicit aim of युनिकोड to transcend the limitations of traditional character encodings such as those defined by the ISO 8859 standard, which are used मा the various countries of the world, but are largely incompatible with each other. One problem with traditional character encodings is that they allow for bilingual कम्प्युटर processing (usually रोमन अक्षरहरु र the local language), but not for multilingual कम्प्युटर processing (कम्प्युटर processing of arbitrary languages mixed with each other).

युनिकोड मा intent encodes the underlying characters र not variant glyphs for such characters. In the case of चाइनिज अक्षरहरुs, this sometimes leads to controversies over what is the underlying character र what is the variant glyph (see Han unification).

युनिकोड's role मा text-processing is to provide a unique code point — not a glyph — for each character. In other words, युनिकोड is used to represent a character मा an abstract way, र leaves the visual rendering (size, shape or style) to another program, such as a वेब ब्राउजर or word processor.

This simple aim is greatly complicated by another aim, which is to provide lossless conversion amongst different existing encodings मा order to ease the transition.

The युनिकोड standard also includes a number of related items, such as character properties, text normalisation forms, र bidirectional display order (for the correct display of text containing both right-to-left scripts, such as अरबी or हेब्रु, र left-to-right scripts).

In 1997 a proposal was made by माइकल इभरसन् to encode the characters of the Klingon language मा Plane 1 of ISO/IEC 10646-2. The proposal was rejected मा 2001 as "inappropriate for encoding" — not because the proposal was technically faulty, but because users of Klingon normally read र write र exchange data मा Latin transliteration. The elvish scripts Tengwar र Cirth from J. R. R. Tolkien's Middle-earth setting were proposed for inclusion मा Plane 1 मा 1993. The draft was withdrawn to incorporate changes suggested by Tolkienists, र is as of 2004 still under consideration.

Mapping र encodings

Standard

The युनिकोड Consortium, based मा California, is the organization that develops the युनिकोड standard. It is an organization open to any company or individual willing to pay the membership dues. Members include virtually all of the main कम्प्युटर software र hardware companies with any interest मा text processing standards, such as Apple Computer, Microsoft, IBM, Xerox, HP, Adobe Systems र many others.

The Consortium first published The युनिकोड Standard (ISBN 0321185781) मा 1991, र continues to develop standards based on that original work. युनिकोड was developed मा conjunction with the International Organization for Standardization र it shares its character repertoire with ISO/IEC 10646. युनिकोड र ISO/IEC 10646 are equivalent as character encodings, but The युनिकोड Standard contains much more information for implementers, covering, मा depth, topics such as bitwise encoding, collation, र rendering, र enumerating a multitude of character properties, including those needed for BiDi support. The two standards also have slightly different terminology.

युनिकोड revision history

• 1991 युनिकोड 1.0
• 1993 युनिकोड 1.1
• 1996 युनिकोड 2.0
• 1998 युनिकोड 2.1
• 1999 युनिकोड 3.0
• 2001 युनिकोड 3.1
• 2002 युनिकोड 3.2
• 2003 युनिकोड 4.0
• 2005 युनिकोड 4.1

Storage transfer र processing

So far, it has only been said that युनिकोड is a means to assign a unique number for all characters used by humans मा written language. How these numbers are stored मा text processing is another matter; problems result from the fact that much software मा the West has so far been written to deal with 8-bit character encodings only, र युनिकोड support has only been added slowly मा recent years. Similarly, मा the East the double-byte character encodings cannot even मा principle encode more than 65,536 characters, र मा practice the limit imposed by the architectures chosen is much lower. This is not enough for the needs of scholars of the Chinese language alone.

The internal logic of much 8-bit legacy software typically permits only 8 bits for each character, making it impossible to use more than 256 code points without special processing, र 16-bit software is limited to some tens of thousands of characters, while युनिकोड is already up to more than 90,000 encoded characters. Several mechanisms have therefore been suggested to implement युनिकोड; which one is chosen depends on available storage space, source code compatibility, र interoperability with other systems.

The mapping methods are called the UTF (युनिकोड Transformation Format) र UCS (Universal Character Set) encodings. Among them are UTF-32, UCS-4, UTF-16, UCS-2, UTF-8, UTF-EBCDIC र UTF-7. The numbers indicate the number of bits मा one unit, for UTF encodings, or bytes, for UCS encodings. In UTF-32 or UCS-4, one unit is enough for any character; मा the other cases, a variable number of units is used for each character. UTF-8 is the de-facto standard encoding for interchange of युनिकोड text with UTF-16 र UTF-32 being used mainly for internal processing.

The युनिकोड byte order mark (BOM) is specified for use at the beginnings of text files मा UCS-2 र UTF-16 encodings. It has been adopted by some software developers for other encodings, including UTF-8, which does not need an indication of byte order. In this case it is an attempt to mark the file as containing युनिकोड text. The BOM is code point U+FEFF, which has the important property of being unambiguously interpretable regardless of which युनिकोड encoding is used. The units FE र FF never appear मा UTF-8, U+FFFE (the result of byte-swapping U+FEFF) is not a legal character, र U+FEFF is the Zero-Width No-Break Space (a character with no appearance र no effect other than preventing formation of ligatures). The same character converted to UTF-8 becomes the byte sequence EF BB BF.

See also: Mapping of युनिकोड characters

Ready-made vs. composite characters

युनिकोड includes a mechanism for modifying character shape र so greatly extending the supported glyph repertoire. This is the use of combining diacritical marks. They are inserted after the main character (it is possible to stack several combining diacritics over the same character). However, for reasons of compatibility, युनिकोड also includes a large quantity of precomposed characters. So मा many cases there are many ways of encoding the same character. To deal with this, युनिकोड provides the mechanism of canonical equivalence.

The situation with Hangul is similar. युनिकोड provides the mechanism for composing Hangul syllables with Hangul Jamo. However, the precomposed Hangul syllables (11,172 of them) are also provided.

The CJK ideographs currently are encoded only मा their precomposed form. Still, most of those ideographs are evidently made up of simpler elements, so मा principle it would be possible to decompose them just as it is done with Hangul. This would greatly reduce the number of required codepoints, while allowing the display of virtually every conceivable ideograph (and so doing away with all problems of the Han unification). A similar idea is used for some input methods, such as Cangjie र Wubi. However, attempts to do this for character encoding have stumbled over the fact that ideographs are not as simply decomposed or as regular as they seem.

Combining marks, like the complex script shaping required to properly render Arabic text र many other scripts, are usually dependent on complex font technologies, like OpenType (by Adobe र Microsoft), Graphite (by SIL International), र AAT (by Apple), by which a font designer includes instructions मा a font telling software how to properly output different character sequences. Another method sometimes employed मा fixed-width fonts is to place the combining mark's glyph before its own left sidebearing; this method, however, only works for some diacritics र stacking will not occur properly.

As of 2004, most software still cannot reliably handle many features not supported by older font formats, so combining characters generally will not work correctly. Hypothetically, ढाँचा:युनिकोड (precomposed e with macron र acute above) र ढाँचा:युनिकोड (e followed by the combining macron above र combining acute above) are identical मा appearance, both giving an e with macron र acute accent, but appearance can vary greatly across software applications.

Also underdots, as needed मा Indic Romanization, will often be placed incorrectly or worse. Sample:

ढाँचा:युनिकोड

Of course, this is मा fact not a weakness मा युनिकोड itself, but only uncovers gaps मा rendering technology र fonts.

Issues

Some people, mostly मा Japan, oppose युनिकोड मा general, claiming technical limitations र political problems मा process, which people working on the युनिकोड standard claim are simply misunderstandings of the युनिकोड standard र the process by which it was created. The most common mistake, according to this view, is confusion between abstract characters र their highly variable visual forms (glyphs). On the other hand, whereas Chinese can readily read most types of glyphs used by Japanese or Koreans, Japanese often can recognize only a particular variant. The strongest denunciation of युनिकोड is at [१] (also see a response, [२]) For example, opponents of युनिकोड sometimes claim even now that it cannot handle more than 65,535 characters, a limitation that was removed मा युनिकोड 2.0. युनिकोड has been decried as a plot against Asian cultures perpetrated by Westerners with no understanding of the characters as used मा Chinese, Korean, र Japanese, मा spite of the presence of a majority of experts from all three countries मा the Ideographic Rapporteur Group. The IRG advises the consortium र ISO on additions to the repertoire र on Han unification, the identification of forms मा the three languages which will be treated as stylistic variations of the same historical character. This unification is one of the most controversial aspects of युनिकोड.

युनिकोड is criticized for failing to allow for older र alternate forms of kanji, which, it is said, complicates the processing of ancient Japanese र uncommon Japanese names, although it follows the recommendations of Japanese scholars of the language र of the Japanese government. There have been several attempts to create an alternative to युनिकोड. [३] Among them are TRON (although it is not widely adopted मा Japan, some, particularly those who need to handle historical Japanese text, favor this), UTF-2000 र Giga Character Set (GCS). It is true that many older forms were not included मा early versions of the युनिकोड standard, but युनिकोड 4.0 contains more than 90,000 Han characters, far more than any dictionary or any other standard, र work continues on adding characters from the early literature of China, Korea, र Japan.

Thai language support has been criticized for its illogical ordering of Thai characters. This complication is due to युनिकोड inheriting the Thai Industrial Standard 620, which worked मा the same way. This ordering problem complicates the युनिकोड collation process [४].

युनिकोड मा use

Operating systems

Despite technical problems र limitations र criticism on process, युनिकोड has emerged as the dominant encoding scheme. Windows NT र its descendants Windows 2000 र Windows XP make extensive use of UTF-16 as an internal representation of text. UNIX-like operating systems such as GNU/Linux, BSD र Mac OS X have adopted UTF-8, as the basis of representation of multilingual text.

E-mail

MIME defines two different mechanisms for encoding non-ASCII characters मा e-mail, depending on whether the characters are मा e-mail headers such as the "Subject:" or मा the text body of the message. In both cases, the original character set is identified as well as a transfer encoding. For e-mail transmission of युनिकोड the UTF-8 character set र the Base64 transfer encoding are recommended. The details of the two different mechanisms are specified मा the MIME standards र are generally hidden from users of e-mail software.

The adoption of युनिकोड मा e-mail has been very slow. Most East-Asian text is still encoded मा a local encoding such as Shift-JIS, र many commonly used e-mail programs still cannot handle युनिकोड data correctly, if they have some support at all. This situation is not expected to change मा the foreseeable future.

Web

Recent web browsers display web pages using युनिकोड if an appropriate font is installed (see Unicode र HTML).

Although syntax rules may affect the order मा which characters are allowed to appear, both HTML 4.0 र XML 1.0 documents are, by definition, comprised of characters from the entire range of युनिकोड code points, minus only a handful of disallowed control characters र the permanently-unassigned code points D800-DFFF, any code point ending मा FFFE or FFFF र any code point above 10FFFF. These characters manifest either directly as bytes according to document's encoding, if the encoding supports them, or they may be written as numeric character references based on the character's युनिकोड code point, as long as the document's encoding supports the digits र symbols required to write the references (all encodings approved for use on the Internet do). For example, the references Δ Й ק م ๗ あ 叶 葉 냻 (or the same numeric values expressed मा hexadecimal, with &#x as the prefix) display on your browser as Δ, Й, ק, م, ๗, あ, 叶, 葉 र 냻—if you have the proper fonts, these symbols look like the Greek capital letter "Delta", Cyrillic capital letter "Short I", Arabic letter "Meem", Hebrew letter "Qof", Thai numeral 7, Japanese Hiragana "A", simplified Chinese "Leaf", traditional Chinese "Leaf", र Korean Hangul syllable "Nyaelh", respectively.

Fonts

Free र retail fonts based on युनिकोड are common, since first TrueType र now OpenType support युनिकोड. These font formats map युनिकोड code points to glyphs.

There are thousands of fonts on the market, but fewer than a dozen fonts attempt to support the majority of युनिकोड's character repertoire; these fonts are sometimes described as pan-युनिकोड. Instead, युनिकोड based fonts typically focus on supporting only basic ASCII र particular scripts or sets of characters or symbols. There are several reasons for this: applications र documents rarely need to render characters from more than one or two writing systems; fonts tend to be resource hogs मा computing environments; र operating systems र applications are becoming increasingly intelligent मा regard to obtaining glyph information from separate font files as they are needed. Furthermore, it is a monumental task to design a consistent set of rendering instructions for tens of thousands of glyphs; such a venture passes the point of diminishing returns for most typefaces.

युनिकोड characters which cannot be rendered are most often displayed as an open rectangle only, to indicate the position of the unrecognized character. Some attempts have been made to provide more information about these characters. The Apple LastResort font will display a substitute glyph indicating the युनिकोड range of the character र the SIL Unicode fallback font will display a box showing the hexadecimal scalar value of the character.

Multilingual Text Rendering Engines

• Uniscribe - Windows
• Apple Type Services for Unicode Imaging - new engine for Macintosh
• WorldScript - old engine for Macintosh
• Pango - open source
• Graphite - (open source renderer from SIL)

Input methods

On Windows XP, any युनिकोड character can be input by pressing Alt, then, with Alt down (and using only the numeric keypad keys), pressing the decimal digits of the युनिकोड characters one after the other. For example, Alt, then, with Alt still down, 9, then 6 र then 0 yields π (Greek lowercase letter Pi). For values less than 256, precede the digits with a 0, to avoid code page translation (see Extended ASCII), e.g. Alt 0, 1, 6, 5 yields ¥.

Word 2003 also allows for entering युनिकोड characters by spelling out the code first, e.g. 014B for the 'ng'-symbol र then hitting 'Alt' plus 'X' to substitute the string to the left by its युनिकोड character.

Macintosh users have a similar feature with an input method called 'Unicode Hex Input', मा Mac OS X र मा Mac OS 8.5 र later: hold down the Option key, र type the four-hex-digit युनिकोड code point. Handling of code-points above 0xFFFF is done by entering a surrogate pair; they will be converted into a single character automatically. Mac OS X (version 10.2 र newer) also has a 'Character Palette', which allows users to visually select any युनिकोड character from a table organized numerically, by युनिकोड block, or by a selected font's available characters.

Gnome2 follows ISO 14755. Hold down Ctrl र Shift र enter the hexadecimal युनिकोड value.

The Opera web browser मा version 7.5 र over allows users to enter any युनिकोड character directly into a text field by typing its hexadecimal code, selecting it, र pressing alt+x.

See also

• Table of Unicode characters, 128 to 999

External links

• The Unicode Consortium
  • Unicode versions: 3.1, 3.2, 4.0, 4.0.1, 4.1
  • new characters, scripts र characters र scripts under investigation
  • Code Charts (PDF)
• UTF-8, UTF-16, UTF-32 Code Charts र a character map (JavaScript)
• The Letter Database Uses forms to present groups मा list or grid format by hexadecimal.
• DecodeUnicode - Unicode Wiki, 50.000 gifs र information about each character
• Example text files using Unicode
• Unicode special character map is similar to the Windows version. Click a symbol to obtain either the named or numeric code for HTML.
• Michael Everson's "Leaks मा the Unicode pipeline: script, script, script…" PDF 2MB
• ConScript Unicode Registry a project to standardize part of the Private Use Area for use with artificial scripts र artificial languages. An explanation of how to propose character names मा Unicode is available here.
• The secret life of Unicode "A peek at Unicode's soft underbelly" Describes problems requiring resolution. Includes links to Unicode resources.
• Tim Bray's Characters vs Bytes explains how the different encodings work.
• The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode र Character Sets (No Excuses!) by Joel Spolsky
• Alan Wood's Unicode Resources Contains lists of word processors with Unicode capability; characters are grouped by type; characters are presented मा lists, not grids.
• Fonts र tools:
  • Unicode fonts र tools for the X Window System
  • Unicode TTF fonts: Arial Unicode MS, Code2000: license info र download link, Junicode: license info र download link, Titus Cyberbit Basic: license info & download link
  • UnicodeChecker, a Unicode character browser for Mac OS X
• Software engineering:
  • International Components for Unicode (ICU) An open source set of libraries that provide robust र full-featured Unicode services for your applications on a wide variety of platforms.
  • The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode र Character Sets (No Excuses!) by Joel Spolsky of JoelonSoftware.com
  • Freedesktop.Org’s Project UTF-8’s purpose is to document र promote proper Unicode support मा free र Open Source software.
• Seeing the entirety of Unicode printed out as a single large poster gives a good feel for the size of the code.